The three leading center-left parties — Shelly Yachimovich’s Labor, Tzipi Livni’s Hatnua and Yair Lapid’s Yesh Atid — are exploring possibilities to work together after the January 22 elections to try to prevent Likud-Beytenu head Benjamin Netanyahu from retaining the prime ministership, or at least to wield the strongest possible hand in coalition negotiations with him.

Efforts to merge at least some of the center-left parties foundered in the weeks before the deadline for submitting party lists for the elections earlier this month. A bid for a Labor-Hatnua alliance made some headway, but collapsed because both Yachimovich and Livni wanted to lead any such merged slate.

But opinion polls showing a gradual fall in support for Netanyahu’s Likud-Beytenu — and a first vague indication that some votes might be moving across the political spectrum from right to left — have energized talk of post-election possibilities on the center-left.

At this stage, surveys give no ammunition to the notion that the center-left might prevail in the elections, but activists see Netanyahu sliding, and believe the center-left may yet have more leverage than had been anticipated just a few weeks ago.

Livni said Friday that, after the elections, she would “attempt to create a front with other partners with the same worldview… with the imperative to replace Netanyahu.”

Channel 2 news on Friday night reported contacts between Labor and Hatnua, and indicated that Yesh Atid was also interested in the possibility of cooperation against Netanyahu after the elections, even though it quoted a Yesh Atid source sneering that Livni — who quit the Knesset when she lost the Kadima party leadership early this year — would probably again bolt politics after the vote.

Specifically, there are three areas under discussion in which a center-left bloc could work together, sources said Friday. They could agree not to recommend that Netanyahu form the next coalition, when asked, by the president after the votes are counted, to name the party leader they wanted to see as prime minister. Less symbolically and more practically, they could act as one bloc in coalition negotiations — agreeing as one on whether or not to enter a Netanyahu-led coalition, in the hope of securing betters terms and achieving greater influence. And they could act as a kind of “super-faction” in the Knesset.

The signs of new energy on the center-left are at least partly a consequence of the relentless slide in support for Netanyahu’s Likud-Beytenu — from 44 seats in polls in October, to 35 and even 33 in polls this weekend.

The Likud and Avigdor Liberman’s Yisrael Beytenu are running on a merged list in the elections. In the last elections they won 42 seats between them — 27 for the Likud and 15 for Yisrael Beytenu. When they announced their merger in October, American political strategist Arthur Finkelstein predicted the joint list would get “at least 42″ seats but said he expected “three to five more.”

Most of the “lost votes” in recent polls are going to the more hardline Jewish Home party.

But in a poll released by Yedioth Ahronoth Friday, the Netanyahu-led right-wing electoral bloc was polled as holding only a 4-seat advantage over the center-left and Arab parties.

The poll gave Likud-Beytenu 33 seats, Labor 17 seats and Jewish Home 12 seats. Lapid’s Yesh Atid, Livni’s Hatnua, and Shas were all tied at 11.

Weekend polls showed the other center-left party, Kadima, which was the biggest party in the last Knesset with 28 seats, now either failing to enter the Knesset at all, or scraping in with only two seats.